1. Field of the Invention
This invention relates generally to gas-flow type circuit breakers, and in particular to an improved arc-quenching arrangement for such circuit breakers, particularly blast piston ("puffer") circuit breakers.
2. Description of the Prior Art
Arc-quenching arrangements for gas-flow type circuit breakers including flow canals for directing an arc-quenching gas to the vicinity of a quenching gap and check valves disposed in the canals for controlling the flow of gas to the quenching gap are described in U.S. application Ser. No. 454,544, filed Mar. 25, 1974, entitled "Arc Quenching Arrangement." Each check valve in such an arrangement is disposed in a flow canal formed in a body of electrical insulation material. The quenching gas utilized is usually sulfur hexafluoride (SF.sub.6), which also serves as an insulating medium.
Gas-flow type circuit breakers are preferred for use in high-voltage electrical installations for extinguishing large arc currents. Typically, several check valves and flow canals are provided in such circuit breakers. The gas flow canals may be configured in the shape of a ring canal having a plurality of spring vanes which function as check valves.
Generally speaking, such a gas-flow arc blasting arrangement is coupled to one of the electrodes of the circuit breaker in a positive, force-transmitting relationship. In one known gas-flow type circuit breaker, gas compression during separation of the electrodes of the breaker is limited by a gas overflow canal running parallel to the quenching gap of the apparatus. The overflow canal couples a high pressure space (in which the arc quenching gas is disposed) with a lower pressure area within the body of insulation material near the quenching gap and contains at least one pressure valve for controlling the flow of gas therethrough. The pressure valve is biased so that the quenching gap is bypassed and the pressure valve within the high pressure space in the housing is exceeded. If such an overpressure occurs, the arc-quenching gas flows directly through the overflow canal to the low pressure region within the insulation body and bypasses the quenching gap.
It has been discovered that the quenching capacity of the arrangement can be adversely affected if, during the time in which the arc to be extinguished decreases to a zero current flow, the heated arc-quenching gas must first be displaced from the space in each flow canal between the check valve and the quenching gap adjacent the electrodes of the apparatus subsequent to the pressure build-up within the breaker apparatus housing and after the opening of the check valve.